Epidemiological studies have identified an association of elevated levels of estrogens with breast cancer development. In particular, the natural hormone, 17(3-estradiol and its catechol metabolites have been implicated in breast cancer development, and it is believed that estrogen catechols cause free radical mediated, direct and/or indirect DNA damage, which may lead to gene mutations and ultimately breast cancer. We have detected several oxidative and other polar DMA adducts in the mammary tissue of rats and in human breast tissues by newly devised 32P-postlabeling/TLC systems. Chromatographic similarity with reference oxidative adducts suggests that tissue DNA adducts originated from free radical-mediation. These results suggest that the adducts may have resulted from redox cycling of 17-3-estradiol metabolites. We hypothesize that combination of chemopreventive agents will provide more effective prevention of breast cancer than individual agents. This will be accomplished by 1) utilizing combination of agents with different modes of action;and 2) by using a novel systemic slow-release device to circumvent toxicity. Our preliminary results by interventions with ellagic acid delivered by systemic slow-release system and diet elicited similar degree of inhibition of 17-3-estradiol-mediated mammary tumorigenesis in the ACI rat model, supporting our working hypothesis. A team of experienced investigators will pursue the following specific studies to meet our goals: 1) Determine the efficacy of selected agents to modulate estrogen-metabolism and DNA repair in vivo. 2) Determine the efficacy of candidate agents to diminish 17-3-estradiol-induced cell proliferation in vivo. 3) Determine the efficacy of candidate agents to inhibit 17-3-estradiol-induced mammary tumorigenesis, and correlate modulation of estrogen metabolism with tumor indices. 4) Determine if combination of agents delivered by the slow-release device will provide more effective inhibition of mammary tumorigenesis compared with the individual agents. The resulting data will reveal that combination of agents working via different arenas can provide more complete prevention of mammary tumors than individual agents, and that the systemic slow-release delivery can circumvent toxicity by significantly reducing the effective dose. The data will also identify pathway(s) that can be targeted for effective prevention of breast cancer, and perhaps other hormonal cancers.